Medium Access Control Layer

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Telematics Chapter 5: Medium Access Control Sublayer

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Application Layer Application Layer

Presentation Layer Presentation Layer

Session Layer Session Layer

Transport Layer Transport Layer

Network Layer Network Layer Network Layer

Univ.-Prof. Dr.-Ing. Jochen H. Schiller Data Link Layer Data Link Layer Data Link Layer

Computer Systems and Telematics (CST) Physical Layer Physical Layer Physical Layer Institute of Computer Science Freie Universität Berlin http://cst.mi.fu-berlin.de Contents

● Design Issues ● Metropolitan Area Networks ● Network Topologies (MAN) ● The Channel Allocation Problem ● Wide Area Networks (WAN) ● Multiple Access Protocols ● Frame Relay (historical) ● Ethernet ● ATM ● IEEE 802.2 – Logical Link Control ● SDH ● Token Bus (historical) ● Network Infrastructure ● Token Ring (historical) ● Virtual LANs ● Fiber Distributed Data Interface ● Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.2 Design Issues

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.3 Design Issues

● Two kinds of connections in networks ● Point-to-point connections OSI Reference Model

● Broadcast (Multi-access channel, Application Layer Random access channel) Presentation Layer

● In a network with broadcast Session Layer connections

● Who gets the channel? Transport Layer

Network Layer ● Protocols used to determine who

gets next access to the channel Data Link Layer ● Medium Access Control (MAC) sublayer Physical Layer

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.4 Network Types for the Local Range

● LLC layer: uniform interface and same frame format to upper layers ● MAC layer: defines medium access

...

LLC IEEE 802.2 Logical Link Control

Layer ANSI ATM ebene 802.3 802.4 802.5 802.6

DataLink X3T9.5 Forum Sicherungs- MAC ... CSMA/CD Token Token ATM LAN (Ethernet) Bus Ring DQDB FDDI Emulation

ISO/OSI ClassicalReale Network Netze Concepts

Both concepts are implemented together in existing networks (as a device driver): 1. Packing of data into frames: error detection during frame transmission and receipt 2. Media Access Control: this contains the frame transmission and the reaction to transmission errors

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.5 Standardization: IEEE

● Institute of Electrical and Electronic Engineers (IEEE) ● Standardization of the IEEE 802.X-Standards for Local Area Networks (www.ieee802.org) – many historical! www.ieee.org

. 802.1 Overview and Architecture of LANs . 802.11 Wireless LAN (WLAN) . 802.2 Logical Link Control (LLC) . 802.12 Demand Priority (HP’s AnyLAN) . 802.3 CSMA/CD (Ethernet) . 802.14 Cable modems . 802.4 Token Bus . 802.15 Personal Area Networks (PAN, . 802.5 Token Ring Bluetooth) . 802.6 DQDB (Distributed Queue Dual Bus) . 802.16 Wireless MAN . 802.7 Broadband Technical Advisory . 802.17 Resilient Packet Ring Group (BBTAG) . 802.18 Radio Regulatory Technical . 802.8 Fiber Optic Technical Advisory Advisory Group (RRTAG) Group (FOTAG) . 802.19 Coexistence Technical . 802.9 Integrated Services LAN Advisory Group (ISLAN) Interface . 802.20 Mobile Broadband Wireless . 802.10 Standard for Interoperable Access (MBWA) LAN Security (SILS) . 802.21 Media Independent Handover

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.6 Network Categories

● Local Area Networks (LAN): 10m - few km, simple connection structure ● Ethernet/Fast Ethernet/Gigabit Ethernet/10Gigabit Ethernet ● Historical: Token Bus, Token Ring LAN ● Historical: FDDI (up to 100 km, belongs rather to LANs) ● Wireless LAN (WLAN, up to a few 100 m) ● Metropolitan Area Network (MAN): 10 - 100 km, city range ● Historical ● DQDB ● FDDI II MAN ● Resilient Packet Ring ● today: Gigabit Ethernet, SDH ● Wide Area Networks (WAN): 100 – 10,000 km, interconnection of subnetworks ● Frame Relay ● ATM WAN ● SDH

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.7 Network Topologies

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.8 Bus

B Terminating resistor Example: Classical Ethernet  

● Bus ● Broadcast Network: if station A intends to send data to station B, the message reaches all connected stations. Only station B processes the data, all other stations ignore it. ● Passive coupling of stations ● Restriction of the extension and number of stations to connected ● Simple, cheap, easy to connect new stations ● The breakdown of a station does not influence the rest of the network

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.9 Star

● Star ● Designated computer as central station: a message of station A is forwarded to station B via the B central station ● Broadcast network (Hub) or point- to-point connections (Switch) ● Expensive central station ● Vulnerability through central station (Redundancy possible) ● N connections for N stations A ● Easy connection of new stations

Example: Fast Ethernet

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.10 Tree

● Tree ● Topology: Connection of several busses or stars ● Branching elements can be active (Router) or passive (Repeater) ● Bridging of large distances ● Adaptation to given geographical structure ● Minimization of the cable length possible

Branch 1 Branch 2

A B C

Repeater Router

Backbone

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.11 Ring

● Ring ● Broadcast Network ● Chain of point-to-point connections B ● Active stations: messages are regenerated by the stations (Repeater) ● Breakdown of the whole network in case of failure of one single station or connection ● Large extent possible A ● Easy connection of new stations ● Only N connections for N stations ● Variant: bidirectional ring Example: Token Ring, FDDI ● stations are connected by two opposed rings

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.12 Meshed Networks

● Fully Meshed Network ● Point-to-Point connections between all stations ● For N stations N(N 1) 2 connections are needed ● Connecting a new station is a costly process ● Redundant paths ● Maximal connection availability through routing integration

Partly meshed network: cheaper, but routing, flow control, and congestion control become necessary (Wide Area Networks)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.13 Examples

● Ethernet (IEEE 802.3, 10 Mbps) ● originally the standard network ● available in an “immense number” of variants

● Token Ring (IEEE 802.5, 4/16/100 Mbps) ● for a long time the Ethernet competitor ● extended to FDDI (Fiber Distributed Data Interface) ● Fast Ethernet (IEEE 802.3u, 100 Mbps) ● at the moment the most widely spread network ● extension of Ethernet for small distances ● Gigabit Ethernet (IEEE 802.3z, 1000 Mbps) ● very popular at the moment; 10 Gbps are already in the planning phase at the moment

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.14 The Channel Allocation Problem

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.15 The Channel Allocation Problem

● The channel allocation problem ● Given N independent stations which want to communicate over a single channel ● Organize the sending order of the stations

Medium . Wire or wireless

● Approaches ● Static channel allocation ● Simple procedures ● Dynamic channel allocation ● Complex procedure, that adapt to changes

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.16 Static Channel Allocation

● Time Division Multiple Access ● Frequency Division Multiple (TDMA) Access (FDMA) ● Each user gets the entire ● Each user gets a portion of the transmission capacity for a fixed transmission capacity for the whole time interval time ● Baseband transmission ● Frequency range ● Broadband transmission

Frequency Frequency

User 1 User 2 Time User 3 1 2 3 1 2 3 1 2 3 Time

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.17 Static Channel Allocation

● Problems with static channel allocation ● Works only for a fixed number of users ● When number of users change, the allocation scheme does not work ● Data traffic is very often bursty, i.e., long time no data and for a short time high data (ok for classical voice communication!) ● Thus, users do not use their allocated channel capacity Most of the channels will be idle most of the time

Dynamic Channel Allocation

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.18 Dynamic Channel Allocation

● Assumptions on dynamic channel allocation ● Station Model ● There are N independent stations (computers) that generate frames for transmission. ● Single channel ● A single channel is available for communication and all stations can transmit and receive on it. ● Collisions ● If two frames are transmitted simultaneously, they overlap and the signals are garbled. ● Time ● Continuous time: No master clock, transmission of frames can begin at anytime. ● Slotted time: Time is divided into discrete intervals called slots. Frame transmissions begin always at the start of a slot. ● Sensing of the medium ● Carrier sense: Stations can sense channel and tell whether it is busy. If so, stations do not start with transmissions. ● No carrier sense: Stations can not sense the channel.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.19 Multiple Access Protocols

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.20 Multiple Access Protocols: ALOHA

● Best known protocol: ALOHA ● Developed on the Hawaiian islands in 1970s: stations are connected by a satellite ● Very simple principle, no coordination: ● Stations are sending completely uncoordinated (random), all using the same frequency ● When two (or more) stations are sending at the same time, a collision occurs: both messages are destroyed. ● Collisions occur even with very small overlaps! ● Vulnerability period: 2 times the length of a frame ● When a collision occurs, frames are repeated after a random time ● Problem: since traffic runs over a satellite a sender only hears after a very long time whether the transmission was successful or not.

Collision

Sender A Sender B

Sender C t

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.21 Multiple Access Protocols: ALOHA

● Problem with ALOHA: even small overlaps result in transmission conflicts. Therefore, often collisions result in many repetitions: ● No guaranteed response times ● Low throughput ● Improvement: Slotted ALOHA ● The time axis is divided into time slots (similar to TDMA, but time slots are not firmly assigned to stations) ● The transmission of a block has to start at the beginning of a time slot ● Fewer collisions, vulnerability period of one frame length ● But: the stations must be synchronized! Collision

Sender A Sender B Sender C t

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.22 Multiple Access Protocols: ALOHA

● Performance of ALOHA ● Assumptions ● Infinite number of interactive users generating data ● Data is generated according to a Poisson distribution ● Poisson process ● Consider a time interval [0,t) ● Random variable X gives the number of events (packets, transmissions, …) in the time interval of length t ● The probability that k events occur in the time t interval is given by

(t)k P(X  k)  et k!

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.23 Multiple Access Protocols: ALOHA

● Performance of ALOHA ● Assumptions ● Data is generated according to a Poisson distribution X with mean G frames/s ● Collided frames are retransmitted ● Probability of k transmission trials per frame time is according to a Poisson distribution with mean G Gk P(X  k)  eG with G  t k!

● Throughput (S) is given by the load (G) and the probability of a successful

transmission (P0)

S = G×P0 ● What is a successful transmission? ● A frame is transmitted successful if no other frames are sent within one frame time G0 P  P(X  0)  eG  eG 0 0!

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.24 Multiple Access Protocols: ALOHA G0 ● Probability of zero frames is: P(X  0)  eG  eG 0! ● Collision time

● ALOHA: tc=2t

● Slotted ALOHA: tc=t ● Throughput -2G Maximum ● ALOHA: S = G P0 = G e ● Slotted ALOHA: S = G P = G e-G . Slotted ALOHA ~36% 0 . ALOHA ~18%

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.25 Multiple Access Protocols: CSMA

● Variant of ALOHA for networks with small distances exists ● Similar to ALOHA: no coordination of the stations ● But: each station which wants to send first examines whether already another station is sending ● If nobody sends, the station begins to send Carrier Sense Multiple Access (CSMA)

● Notice ● This principle only works with networks having a short transmission delay ● Application of this principle for satellite systems is not possible, because there would be no chance to know whether a conflict occurred before the end of the transmission ● Advantages: simple, because no master station and no tokens are needed; nevertheless good utilization of the network capacity ● Disadvantage: no guaranteed medium access, a large delay up to beginning a transmission is possible

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.26 Multiple Access Protocols: CSMA

● Persistent and Nonpersistent CSMA ● 1-persistent CSMA ● When a station has data to send, it first listens to the channel. ● If channel busy, the station waits until it becomes idle. ● When channel is idle, station transmits a frame. ● When a collision occurs, the station waits a random amount of time and starts all over again. ● 1-persistent = station transmits with probability of one if channel idle ● Nonpersistent CSMA ● When channel is busy, station waits a random time, and repeats ● p-persistent CSMA ● Applied in slotted channels (slotted ALOHA) ● If channel idle, station transmits with probability p in current slot and with probability (1-p) it defers until next slot ● If next slot is idle, the station again transmits with probability p and defers with (1-p)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.27 Multiple Access Protocols: CSMA

● CSMA with Collision Detection: CSMA/CD ● Basis of classical Ethernet (not today’s versions with star topology!) ● A station who detects a collision stops immediately transmitting ● Afterwards it waits a random time and tries again

Frame Frame Frame Frame

Transmission Contention Idle period period period

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.28 Multiple Access Protocols Collision-Free Protocols

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.29 Collision-Free Protocols: Reservation Protocols

● Communication follows in a two-phase scheme (alternating phases) ● Phase 1: Reservation ● In the reservation phase the sender makes a reservation by indicating the wish to send data (or even the length of the data to be sent) ● Phase 2: Transmission ● In the transmission phase the data communication takes place (after successful reservation) ● Advantage: very efficient use of the capacity ● Disadvantage: ● Delay by two-phase procedure ● Often a master station is needed, which cyclically queries all other stations whether they have to send data. The master station assigns sending rights.

● Techniques for “easy” reservation without master station: ● Explicit reservation ● Implicit reservation

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.30 Collision-Free Protocols: Bit-Map Protocol

● Uses two frame types: ● reservation frame (very small) in the first phase ● data frame (constant length) in the second phase ● Variant 1: Without contention ● Only suitable for small number of users ● Each user i is assigned the i-th slot in the reservation frame. If it wants to send data, it sets the i-th bit in the reservation frame to 1. ● After the reservation phase, all stations having set their reservation bit can send their data in the order of their bits in the reservation frame.

reservation data frames of stations frame having reserved

1 1 1 2 5 7 1 4 1 1 1 1

This procedure is called Bit-Map Protocol

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.31 Collision-Free Protocols: Bit-Map Protocol

● Variant 2: With contention ● For higher number of users ● The reservation frame consists of a limited number of contention slots (smaller than the number of participating stations) ● Users try to get a contention slot (and by that make a reservation for a data slot) by random choice, writing their station number into a slot ● If there is no collision in the reservation phase, a station may send.

reservation frame data frames of stations with contention slots having reserved 22 31 5 22 31 34

17 45 4 17 45 4 11 11 25 12

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.32 Collision-Free Protocols: Binary Countdown

● Binary Countdown ● For large number of stations ● Binary station addresses, all addresses to be the same length Bit time ● A station wanting to use the Stations 0 1 2 3 channel broadcasts its address as a 0010 0 binary string starting with the high- order bit 0100 0 ● The bits from different stations are 1001 1 0 0 ORed 1010 1 0 1 0 ● As soon as a station sees that a Result 1 0 1 0 high-order bit position that is 0 in its address has been overwritten to a 1, gives up ● Example: four stations with addresses 0010, 0100, 1001, 1010

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.35 Multiple Access Protocols Limited Contention Protocols

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.36 Limited Contention Protocols: Adaptive Tree Walk

● Adaptive Tree Walk Protocol ● Stations are the leaves of a binary tree ● In the first contention slot following a successful frame, slot 0, all stations (A-H) are permitted to try to acquire the channel ● If collision, during slot 1 only stations under node 2 (A-D) may compete ● If one gets the channel, next slot is reserved for stations under node 3 (E-H) ● If collision, during slot 2, only stations under node 4 (A, B)

2 3

4 5 6 7

A B C D E F G H

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.37 Coordination by using a Token

● Introduction of a token (determined bit sequence) ● Only the owner of the token is allowed to send 1 ● Token is cyclically passed on between all stations ● particularly suitable for ring topologies 5 2 ● Token Ring (4/16/100 Mbps)

4 3

● Characteristics Passing on of the token ● Guaranteed accesses, no collisions ● Very good utilization of the network capacity, high efficiency ● Fair, guaranteed response times ● Possible: multiple tokens ● But: complex and expensive

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.38 Ethernet

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.39 Ethernet

● Evolution of Ethernet ● 1970s on Hawaii ALOHANET (Abramson) ● Connecting computers on islands over radio ● Two channels ● Uplink shared by the clients (collision may occur) ● Downlink exclusively used by main computer ● Packets are acked by main computer ● Good performance under low traffic, but bad under heavy load ● 1970's: experimental network on the basis of coaxial cables, data rate of 3 Mbps. Developed by the Xerox Corporation as a protocol for LANs with sporadic but bursty traffic. ● 1976 Ethernet by Robert Metcalf at Xerox Parc ● Ether: luminiferous ether through which electromagnetic radiation was thought to propagate ● Improvements to ALOHANET ● Listen to the medium before transmitting

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.40 Ethernet

● 1978: Development of 10 Mbps-variant by Digital Equipment Corporation (DEC), Intel Corporation, and Xerox (DIX-standard) ● 1983: DIX-standard became the IEEE 802.3 standard ● Metcalf founded 3Com ● Sold many, many million Ethernet adapters

● Original Ethernet structure: ● Bus topology with a maximum segment length of 500 meters, connection of a maximum of 100 passive stations. ● Repeaters are used to connect several segments. ● Most common medium: Copper cable. ● In addition, optical fibers are used (the segment length increases). ● Early 90's: the bus topology is displaced more and more by a star topology, in which a central hub or switch (based on Twisted Pair or Optical Fiber) realizes connections to all stations. ● The switch offers the advantage that several connections can run in parallel.

Univ. -Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.41

Ethernet - historical

● Based on the standard IEEE 802.3 “CSMA/CD”

(Carrier Sense Multiple Access/Collision Detection)

● Several (passive) stations - one shared medium (random access) ● Originally, bus topology:

1. Is the medium available? (Carrier Sense) ?

2. Data transmission ?

3. Check for collisions (Collision Detection) If so: send jamming signal and stop transmission. Go on with binary exponential backoff algorithm

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.42 Carrier Sense Multiple Access

Principle: . listen to the medium before sending . send only if the medium is free

1. Station S1 sends

Message from S1

Signal expansion 2. Station S2 also wants Expansion of the signal on also in other to send but notices that S the medium direction a transmission already 2 takes place.

. Advantages: simple, since no mechanisms are needed for the coordination; with some extensions nevertheless a good utilization of the network capacity

. Disadvantage: no guaranteed access, a large delay before sending is possible

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.43 Problem with CSMA

Problem: the message which is sent by S1 spreads with finite speed on the medium. Therefore, it can be that S2 only thinks that the medium would be free, although S1 already has begun with the transmission. It comes to a collision: both messages overlap on the medium and become useless.

Note: the signals from S1 and S2 also expand to the left direction, S not shown here for 1 simplification of the figure.

1. Station S1 sends

Message from S1 Message from S2

2. Station S2 also Expansion of the signal on wants to send and the medium thinks the medium S2 would be free.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.44 Detection of Collisions

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) ● Principle: ● like CSMA ● additionally: stop the transmission if a collision occurs

Maximum distance in the network S1 S2

S1 sends

S2 sends

S2 detects the conflict and stops. S1 detects the conflict and knows that the transmission Transmission of a has to be repeated. jamming signal. Time Only small overlapping, but nevertheless both messages are destroyed

Note: with increasing expansion of the network the risk of a conflict also increases. Therefore, this technology is suitable only for “small” networks (Ethernet)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.45 Data transmission with CSMA/CD

● When does the collision detection in CSMA/CD work correctly? ● The maximum time for the detection of a collision is about twice as long as the signal propagation delay on the medium. ● First compromise: one wants to create large networks, but although to have a small probability of collisions … ● Result: the maximum expansion of the network is specified as 2,500m. ● At a signal speed of approximately 2,00,000 km/s (5 µs/km) the maximum signal propagation delay (with consideration of the time in repeaters) is less than 25 µs. ● The maximum conflict duration thereby is less than 50 µs. To be sure to recognize a collision, a sending station has to listen to the medium at least for this time. ● Arrangement: a station only listens to the medium as long as it sends data. ● Based on a transmission rate of 10 Mbps a minimum frame length (64 byte) was defined in order to make a collision detection possible. ● The 64 bytes need the maximum conflict duration of 50 µs

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.46 Performance of CSMA/CD

● The performance of Ethernet systems depends on the vulnerability part a:

Data still Data already sent to send

● a is the fraction of a frame which the sender has to transmit until the first bit crossed the network ● If a station begins to send during the time a needs to cross the network, a conflict arises ● The smaller a is, the better is the performance of the network ● a is small … ● when the network is small ● when frames are large ● when capacity is low ● Conclusion: the best network has nearly zero size, nearly zero capacity, and a station should never stop sending.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.47 Ethernet: Encoding on the Physical Layer

● No directly usage of binary encoding with 0 volts for a 0-bit and 5 volts for a 1-bit ● Synchronization problems ● Manchester Encoding ● Transition in the middle of a bit ● The high signal is at +0.85 volts and the low signal at -0.85 volts ● Disadvantage: twice bandwidth, i.e., to send 10Mbps, 20MHz is required

0 1 0 1 1 0 0 1 + 0.85 volt 0 volt - 0.85 volt

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.48 The Ethernet Frame Byte 7 1 6 6 2 0-1500 0-46 4 Preamble SFD DA SA L/T Data Padding FCS

1 2 3 4 5 6 7 8

1: 7 byte synchronization 5: 2 byte length (IEEE 802.3)/type Each byte contains 10101010 (Ethernet) • In 802.3: Indication of the length of the 2: 1 byte start frame delimiter (SFD) data field (range: 0 - 1500 byte) Marking of the begin of the frame by • In Ethernet: identification of the upper the byte 10101011 layer protocol, e.g., IP, IPX, etc.

3: 6 (2) byte destination address 6: (0 – 1500) byte data MAC address of receiver 7: (0 – 46) byte padding 4: 6 (2) byte source address • Filling up of the frame to at least 64 byte MAC address of sender (smaller fragments in the network are discarded, exception the jamming signal) 8: 4 byte Frame Check Sequence (FCS). Use of a cyclic code (CRC).

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.49 The Ethernet Frame

● Preamble: marks a following transmission and synchronizes the receiver with the sender. ● The Start-of-Frame-Delimiter (resp. the two successive ones) indicates that finally data are coming. ● Destination address: the first bit determines the kind of receiver: ● First bit 0: an individual station ● First bit 1: a group address (multicast) ● Broadcast is given by 11…1 ● Length(/Type): In IEEE 802.3 a value ≤1500 indicates the length of the data part. ● In Ethernet, the meaning is changed, identifying the layer-3 protocol to which the data have to be passed. ● For distinction from IEEE 802.3, only values from 1536 are permitted. ● FCS: Checksum, 32-bit (CRC). ● It covers the fields DA, SA, length/type, data/padding. ● Error detection

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.50 The Ethernet Frame: Addresses

● MAC address 6 byte 1 2 3 4 5 6 ● Originally invented at Xerox PARC ● Unicast or ● Multicast Organizationally Unique Network Interface ● Broadcast Identifier (OUI) Controller (NIC) Specific

● Administrative b1 b2 b3 b4 b5 b6 b7 b8 ● Globally unique, assigned by IEEE ● Locally administered 0: unicast 1: multicast ● Tools 0: globally unique ● Windows: getmac, ipconfig /all, arp -a 1: locally administered ● Linux: ifconfig, cat /proc/net/arp ● http://www.heise.de/netze/tools/mac-adressen

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.51 The Ethernet Frame: Network Analyzer

● Network packet analyzer: Wireshark ● http://www.wireshark.org/

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.52 Ethernet Resolving Transmission Conflicts

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.53 Resolving Transmission Conflicts

● What to do after a collision detection? ● Different categories of reaction methods

● Non-persistent (example: ALOHA): ● After a conflict, wait a random time afterwards start a new transmission ● Problem: possibly inefficient utilization of the medium

● 1-persistent ● Idea: it is very unlikely that during a current transmission two or more new messages appear ● Start the next transmission attempt as soon as possible, thus as soon as the channel is free or becomes free after having been busy / after a conflict ● Problem: Subsequent conflicts!

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.54 Resolving Transmission Conflicts

● p-persistence: ● In this variant conflicts between concurrently waiting messages should be avoided ● In a free channel transmission takes place only with probability p ● In case of a conflict, a message needs on the average 1/p attempts

● But: how to select p? ● p large  high risk for subsequent conflicts ● p small  long waiting periods ● p = 0  not possible ● p = 1  1-persistent

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.55 Resolving Transmission Conflicts

● Performance of Ethernet ● Ethernet at 10 Mbps with 512-bit slot times ● Assumptions ● T : Time to transmit a frame ●  : Propagation on cable ● A: Probability that a station gets the channel T Channel efficieny  2 T  A

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.56 Resolving Transmission Conflicts

Compared to ALOHA, CSMA in any form has a good efficiency (based on a mathematical modeling of network traffic)

Nevertheless for Ethernet a further procedure was developed: the Binary Exponential Backoff mechanism

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.57 Resolving Collisions in Ethernet: Binary Exponential Backoff

● Binary Exponential Backoff (BEB) ● In order to avoid the simultaneous repetition of transmissions after a collision (subsequent collision), a random waiting period is drawn from a given interval. ● The interval is kept small, in order to avoid long waiting periods up to the repetition. ● Thus, the risk of a subsequent conflict is high. ● If it comes to a further collision, the interval before the next attempt is increased, in order to create more clearance for all sending parties. ● The waiting period is determined as follows: ● After i collisions, a station throws a random number x from the interval [0, 2i-1] ● After 10 collisions, the interval remains fixed with [0, 210-1] ● After the 16-th collision a station aborts the transmission completely ● As soon as the medium is free, the sender waits for x time slots, whereby a time slot corresponds to the minimum Ethernet frame length of 512 bits (for a 10 Mbps Ethernet this corresponds to the maximum conflict period of 51,2 µs). ● After the x-th time slot the station becomes active with carrier sense.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.58 Resolving Collisions in Ethernet: Binary Exponential Backoff

● Advantage: ● Short waiting periods (by small interval) if not much traffic is present ● Distribution of repetitions (by large interval) if much traffic is present

● Disadvantage: ● Stations having a subsequent conflict during a repetition have to draw a random waiting period from an interval twice as large. If they are having a further conflict, the interval again is doubled, … ● Thus, single stations can be disadvantaged.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.59 Ethernet Types of Ethernet

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.60 Ethernet

Based on IEEE 802.3 “CSMA/CD” http://www.ethernetalliance.org

4 classes of Ethernet variants: Still partly in use

● Standard Ethernet  10 Mbps Today the most common used variant ● Fast Ethernet  100 Mbps Also used in MANs

● Gigabit Ethernet  1,000 Mbps Standardized not long ago ● 10Gigabit Ethernet  10,000 Mbps

Ethernet became generally accepted within the LAN range. It is used in most LANs as infrastructure:

● It is simple to understand, to build, and to maintain

● The network is cheap in the acquisition

● The topology allows high flexibility ● No compatibility problems, each manufacturer knows and complies with the standard

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.61 Ethernet Parameters

Parameter Ethernet Fast Gigabit Ethernet Ethernet

Maximum expansion ≤ 2500 meters 205 meters 200 meters

Capacity 10 Mbps 100 Mbps 1000 Mbps

Minimum frame 64 byte 64 byte 520 byte length Maximum frame 1526 byte 1526 byte 1526 byte length 4B/5B code, Manchester Signal representation 8B/6T code, 8B/10B code,… code … Max number of 5 2 1 repeaters Additionally, for the jamming a certain 4 byte pattern is sent.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.62 Naming of Ethernet Variants

Indication of the used Ethernet variant by 3 name components:

1. Capacity in Mbps (10, 100, 1000, 10G)

2. Transmission technology (e.g. Base for baseband, Broad for broadband) 3. Maximum segment length in units of the medium used by 100 meters, resp. type of medium

Examples: ● 10Base-5: 10 Mbps, baseband, 500 meters of segment length

● 100Base-T2: 100 Mbps, baseband, two Twisted Pair cables (i.e. two cores) ● 1000Base-X: 1000 Mbps, baseband, optical fiber

Some parameters depend on the variant, e.g., the minimum frame length (because of different signal propagation delay):

● 1000Base-X: minimum frame length of 416 bytes ● 1000Base-T: minimum frame length of 520 bytes

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.63 Ethernet Basic Ethernet (10Base) - historical

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.64 Ethernet - Configurations

up 100 to 100Stationen 100 Stations Stationen  100 Stationen

Segment1Segment1 Segment1 RepeaterRepeater  50 m  50 m Repeater  50 m Segment2Segment2 Segment2  2.5 m  2.5 m TerminatorTerminator  2.5 m Terminator  500 m 500 m  500 m Grundeinheit: Segment BasicGrundeinheit: configuration: Segment segment ConnectionKopplungKopplung ofzweier segments zweierSegmente through Segmente a repeater Grundeinheit: Segment Kopplung zweier Segmente

50 m 500 m 50 m 500 m 500 m 500 m 50 m 500 m 500 m 50 m 50 m 50 m 50 m 50 m 50 m 50 m 50 m 50 m 500 m 500 m 500 m Glasfaserkabel 50 m 50 m50 m 50 m GlasfaserkabelOptical fiber 50 m 50 m Glasfaserkabel 1000 m1000 m 1000 m EthernetEthernet maximaler maximaler Länge Länge EthernetEthernet withmaximaler maximum Länge range

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.65 10Base-2 (Cheapernet)

● Cheap coaxial cable (flexible) ● Thin Ethernet ● Terminals are attached with BNC connectors ● Max. 5 segments (connected by repeaters) ● Max. 30 stations per segment ● At least 0.5 m distance between connections ● Max. 185 m segment length ● Maximum expansion 925 m

BNC plug

Coaxial cable

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.66 10Base-2 (Cheapernet)

Coax cable

Branch connection (T-Stück)

Terminator

Transceiver

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.67 10Base-T (Twisted Pair)

● Star topology using twisted pair: several devices are connected by a hub ● Devices are attached by a RJ-45 plug (Western plug), however only 2 of the 4 pairs of the cables are used ● Cable length to the hub max. 100 m ● Total extension thereby max. 200 m ● Long time the most commonly used variant

Hub

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.68 10Base-F

● Ethernet with Fiber optics ● Expensive ● Excellent noise immunity ● Used when distant buildings have to be connected ● Often used due to security issues, since wiretapping of fiber is difficult

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.69 Ethernet Fast Ethernet

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.70 Fast Ethernet

● Principle: still use the Ethernet principles, but make it faster ● Compatibility with existing Ethernet networks ● 100 Mbps as data transmission rate, achieved by better technology, more efficient codes, utilization of several pairs of cables, switches,… ● Result: IEEE 802.3u, 1995 ● Problem ● The minimum frame length for collision detection with Ethernet is 64 byte. ● With 100 Mbps the frame is sent about 10 times faster, so that a collision detection is not longer ensured. ● Result: for Fast Ethernet the expansion had to be reduced approx. by the factor 10 to somewhat more than 200 meters … ● Therefore, its concept is based on 10Base-T with a central hub/switch. ● Auto configuration ● Negotiation of speed ● Negotiation on communication mode (half-duplex, full-duplex)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.71 100Base-T (Fast Ethernet)

● 100Base-T4 ● Twisted pair cable (UTP) of category 3 (cheap) ● Uses all 4 cable pairs: one to the hub, one from the hub, the other two depending upon the transmission direction ● Encoding uses 8B/6T (8 bits map to 6 trits) ● 100Base-TX ● Twisted pair cable (UTP) of category 5 (more expensive, but less absorption) ● Uses only 2 cable pairs, one for each direction ● Encoding uses 4B/5B ● The most used 100 Mbps version ● 100Base-FX ● Optical fiber, uses one fiber per direction ● Maximum cable length to the hub: 400 meters ● Variant: Cable length up to 2 km when using a switch. Hubs are not permitted here, since with this length no collision detection is possible anymore. In the case of using a good switch, no more collisions arise!

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.72 Ethernet Gigabit Ethernet

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.73 Gigabit Ethernet

● 1998 the IEEE standardized the norm 802.3z, “Gigabit Ethernet” ● Again: compatibility to (Fast) Ethernet has to be maintained! ● Problem: for collision detection a reduction of the cable length to 20 meters would be necessary … “Very Local Area Network” ● Auto configuration as in Fast Ethernet (data, half-duplex, duplex, …) ● Therefore, the expansion remained the same as for Fast Ethernet – instead a new minimum frame length of 512 byte was specified by extending the standard frame by a ‘nodata’ field (after the FCS, because of compatibility to Ethernet). This procedure is called Carrier Extension. ● It is added by the hardware, the software part does not know ● When a frame is passed on from a Gigabit Ethernet to a Fast Ethernet, the ‘nodata’ part is simply removed and the frame can be used like a normal Ethernet frame.

Length PRE SFD DA SA DATA Padding FCS nodata /Type

Preamble Start Del. 7 byte 1 byte

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.74 Gigabit Ethernet

● With Gigabit Ethernet the sending of several successive frames is possible (Frame Bursting) without using CSMA/CD repeatedly. ● The sending MAC controller fills the gaps between the frames with “Interframe-bits” (IFG), thus for other stations the medium is occupied.

MAC frame (including nodata field) IFG MAC frame IFG …. MAC frame

● Under normal conditions, within Gigabit Ethernet no more hubs are used. In the case of using a switch no more collisions occur, therefore the maximum cable length is only determined by the signal absorption.  usage for backbone connections in the MAN area

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.75 1000Base-T/X (Gigabit Ethernet)

● 1000Base-T ● Based on Fast Ethernet ● Twisted pair cable (Cat. 5/6/7, UTP); use of 4 pairs of cables ● Segment length: 100 m ● 1000Base-CX ● Shielded Twisted Pair cable (STP); use of 2 pairs of cables ● Segment length: 25 m ● Not often used ● 1000Base-SX ● Multimode fiber with 550 m segment length ● Transmission on the 850 nm band Added later: ● 1000Base-LX 1000Base-LH ● Single- or multimode over 5000 m • Single mode on 1550 nm ● Transmission on 1300 nm • Range up to 70 km • MAN!

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.76 Ethernet: 10-Gigabit Ethernet

● 10-Gigabit Ethernet, IEEE 802.3ae ● (First) only specified for optical fiber (LX or SX) ● Star topology using a switch ● CSMA/CD is no longer used since no collisions can occur (but nevertheless implemented for compatibility with older Ethernet variants regarding frame format and size …) ● It may also be used also in the MAN/WAN range: 10 - 40 km (Mono mode) ● Most important change: two specifications on physical layer (PHY) ● One PHY for LANs with 10 Gbps ● One PHY for WANs with 9,6215 Gbps (for compatibility with SDH/SONET, see Wide Area Networks)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.77 10G Ethernet: Variants

Wavelength Range Name Type PHY Coding Fiber [nm] [m]

10GBase-SR serial 850 LAN 64B/66B Multimode 26 – 65

10GBase-LR serial 1310 LAN 64B/66B Singlemode 10,000 10GBase-ER serial 1550 LAN 64B/66B Singlemode 40,000

Singlemode 10,000 10GBase-LX4 WWDM 1310 LAN 8B/10B Multimode 300

10GBase-SW serial 850 WAN 64B/66B Multimode 26 – 65 10GBase-LW serial 1310 WAN 64B/66B Singlemode 10,000

10GBase-EW serial 1550 WAN 64B/66B Singlemode 40,000

S: short serial: “normal” transmission L: long WWDM: Wide Wavelength Division Multiplex E: extended

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.78 Wavelength Division Multiplexing (WDM)

Technical principle Wavelength Division Multiplexing: transmit data using four different wavelengths in parallel:

1 1

2 MUX 2

 1 + 2 + 3 +4 

3 DEMUX 3

4 4

Data are distributed to four wavelengths – how to apply this concept to copper cables?

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.79 Are Variants for Twisted Pair possible?

● Some years ago: no, impossible! ● But now e.g.: ● IEEE 802.3ak: 10GBASE-CX4 (Coax) ● Four pairs of cable for each direction ● Cable length of up to 15 meters … ● IEEE 802.3an: 10GBASE-T (Cat. 6/7 TP) ● Cat6 (50 meters) or Cat7 (100 meters) cabling ● Use of all 8 lines in the TP cable – in both directions in parallel! ● Filters for each cable to separate sending and receiving signal ● Layer 1: Variant of Pulse Amplitude Modulation (PAM) with 16 discrete levels between -1 and +1 Volt (PAM16) ● MAC-Layer: keep old Ethernet-Formats …

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.80 And what’s next?

● Maybe combined with full optical networks? ● Optical multiplexers, optical switches ● But at the moment only tested in labs, expensive

● 100G-Ethernet under work (http://www.ethernetalliance.org) ● Data rates from 40G to 100G – currently under test (40GBASE, 100GBASE) ● E.g. IEEE 802.3bg: 40 Gbit/s optical, 802.3bj copper cable! ● Variants for 100 m and 10 km with duplex communication

● Ethernet is still developing (http://www.ieee802.org/3/) We have a number of active projects as listed below: IEEE P802.3 (IEEE 802.3bh) Revision to IEEE Std 802.3-2008 Task Force. IEEE P802.3.1 (IEEE 802.3.1a) Revision to IEEE Std 802.3.1-2011 Ethernet MIBs TF. IEEE P802.3bj 100 Gb/s Backplane and Copper Cable Task Force. IEEE 802.3 Next Generation 100 Gb/s Optical Ethernet Study Group. IEEE 802.3 Extended EPON Study Group. IEEE 802.3 EPON Protocol over a Coax (EPoC) PHY Study Group.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.81 IEEE 802.2: Logical Link Control Revisited for Ethernet

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.82 IEEE 802.2: Logical Link Control

● Ethernet and IEEE 802.3 protocols offer only best effort ● Unreliable datagram service (No acks) ● What to do if error-control and flow-control is required? ● Logical Link Control (LLC) ● Runs on top of Ethernet and other IEEE 802.3 protocols ● Provides a single frame format and interface to the network layer ● Hides differences between the protocols ● Based on HDLC ● LLC provides ● Unreliable datagram service ● Acknowledged datagram service ● Reliable connection oriented service ● LLC header contains ● Destination access point  Which process to deliver? ● Source access point ● Control field  Seq- and ack-numbers

Univ.- Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.83 IEEE 802.2: Logical Link Control

● Relationship between Network Layer, LLC, and MAC ● Network layer passes packet to LLC ● LLC adds header with sequence number and ack number  packet is inserted into the payload of a frame

Network Layer Packet

Data LLC LLC Packet Link Layer MAC MAC LLC Packet MAC

Physical Layer

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.84 IEEE 802.2: Logical Link Control

Preamble SFD DA SA L/T Data Padding FCS

Byte 1 1 1 or 2 DSAP SSAP Control Information

Bit 7 7 I/G DSAP Value C/R SSAP Value

DSAP Destination Service Access Point SSAP Source Service Access Point I/G Individual/Group C/R Command/Response

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.85 Token Bus Basic principle of interest – standard itself is historical

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.86 Token Bus

● Token Bus ● LAN with ring topology ● Token = Small frame, that circulates ● Only the node who possesses the token may send ● One example for a token network: IEEE 802.4 “Token Bus” ● All stations should be treated equally, i.e., they have to pass the token cyclically ● For this: logical ordering of all stations into a ring ● In a bus topology, the ordering is according the station addresses

49 62 17 33

12 42 21 5 15

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.87 Token Bus

● Application Area ● Mainly for industrial applications ● Forced by General Motors for their Manufacturing Automation Protocol standardization effort ● Usage e.g. as a field bus (Feldbus in German) in industrial environments with a high degree of noise. ● Purpose: e.g. roboter control; a few masters, many slaves (they only listen). ● Data rate is not that important, but guarantees in response times are necessary (not possible with Ethernet).

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.88 But… “Industrial Ethernet”

● The Token-Bus approach is more and more displaced by Ethernet variants, e.g.: ● EtherCAT (since 2003, http://www.ethercat.org/) ● Fast Ethernet based on a bus, star, or tree topology (very flexible) ● Uses TP or optical fiber as medium ● Synchronization necessary between all stations ● A master station polls the other stations with a single Ethernet frame – each station has its one time slot to read out/write in data ● Ethernet Powerlink (http://www.ethernet-powerlink.org/) ● Introduction of time slots and a cyclic timing schedule ● Whole time axis is divided into isochronous and asynchronous phases ● Isochronous: for time-critical data transfer ● Asynchronous: for non-time-critical data transfer ● A managing node assigns time slots (in both phases!): in the isochronous phase to all stations, in the asynchronous phase to one particular station

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.89 Token Ring Basic principle of interest – standard itself is historical

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.90 Token Ring

● Token Ring 1 ● LAN with ring topology ● Token = Small frame, that circulates k 2 ● Only the node who possesses the token may send ● Based on the standard IEEE 802.5 “Token Ring” ● The stations share a ring of point-to-point connections … 3 ● The token is cyclically passed on ● particularly suitable for rings Passing on the token ● Token Ring (4/16/100 Mbps) ● Mainly supported by IBM ● Characteristics: ● Guaranteed access, no collisions ● Fair, guaranteed response times ● Possible: multiple tokens ● However: complex and expensive

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.91 Token Ring

● Performance ● Under light load: inefficient, since a station has to wait for the token ● Under heavy load: efficient and fair ● Round robin fashion transmission of stations ● Disadvantage ● Token maintenance ● Lost token can block the network ● Duplication of token ● Monitor station observes the ring ● Central entity

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.92 CSMA/CD vs. Token Bus vs. Token Ring

● CSMA/CD ● Token Bus ● Token Ring ● Advantages ● Advantages ● Advantages ● Widely deployed, high ● More deterministic than ● full digital expertise and experience CSMA/CD ● Automatic recognition and ● Simple protocol ● Short frames possible elimination of cable ● Installation of stations ● Provides priorities problems by wiring-centers during operation (plug-and- ● Provides guarantees ● Provides priorities play) ● Short frames possible, ● Passive cable frame length restricted by token hold time ● Low delay by low traffic

● Good performance by high

load

● Disadvantages ● Disadvantages ● Disadvantages ● Analogous components, min. ● Protocol is complicated ● Central monitor frame length 64 byte, max. ● Lost tokens may cause big ● Delay by low load frame length 1500 byte problems ● Problems at the monitor ● Probabilistic, no priorities ● Analog components may affect the whole ring ● Limited cable length ● Long delay due to token ● Poor performance by high exchange load

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu -berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.93 Token Ring vs. CSMA/CD

Mean Delay 10 Data rate: 10 Mbps [ms] Frame length: 1500 byte Cable length: 2.5 km 8 Number of stations: 100 CSMA/CD (unlimited Delay) 6 Token Ring (Delay is limited) 4

0 (normalized) 0.0 0.2 0.4 0.6 0.8 1.0 Throughput

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.94 Fiber Distributed Data Interface (FDDI) Basic principle of interest – standard itself is historical

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.95 Fiber Distributed Data Interface (FDDI)

● FDDI is a high performance token ring LAN based on optical fibers ● ANSI standard X3T9.5 ● Data rates of 100 Mbps ● Range of up to 200 km (MAN?) ● Support of up to 1000 stations, with distances of maximally 2 km ● Often used as Backbone for small LANs

FDDI 802.5 802.3 LAN LAN

● Successor: FDDI-II, supports besides normal data also synchronous circuit switched PCM data (speech) and ISDN traffic ● Variant: CDDI (Copper Distributed Data Interface), with 100 Mbps over Twisted Pair

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.96 Structure of FDDI

Wiring within FDDI: 2 optical fiber rings with opposite transmission direction

● During normal operation, only the primary ring is used, the secondary ring remains in readiness ● If the ring breaks, the other one (also called protection ring) can be used. ● If both rings break or if a station fails, the rings can be combined into only one, which has double length:

Two classes of stations exist: DAS (Dual Attachment Station) can be attached to both rings, the cheaper SAS (Single Attachment Station) are only attached to one ring.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.97 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.98 Structured Cabling

● Why do we need a structured cabling?

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.99 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.100 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.101 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.102 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.103 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.104 Structured Cabling

● Structured cabling: Partitioning of a network, i.e., cabling infrastructure, which is connected to a backbone or a central switch ● Each user outlet is cabled to a communications closet using individual cables ● In the communications closet the user outlets terminate on patch panels ● Patch panels are mounted usually on 19“ racks

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.105 Structured Cabling

● Advantages of structured cabling ● Consistency ● Usage of the same cabling systems for data, voice, and video ● Support for multi-vendor equipment ● A standard based cable system will support equipment from different vendors ● Simplify modifications ● Supports the changes in within the system, e.g., adding, changing, and moving of equipment ● Simplify troubleshooting ● Problems are less likely to down the entire network and simplifies the isolation and fixing of problems ● Support for future applications ● Support for fault isolation ● By dividing the entire infrastructure into simple manageable blocks, it is easy to test and isolate specific points of fault and correct them

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.106 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.107 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.108 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.109 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.110 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.111 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.112 Structured Cabling

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.113 Wide Area Networks (WAN)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.114 Wide Area Networks

● Characteristics of Wide Area Networks ● Bridging of any distance ● Usually for covering of a country or a continent ● Topology is normally irregular due to orientation to current needs. ● Therefore, not the shared access to a medium is the core idea, but the thought “how to achieve the fast and reliable transmission of as much data as possible over a long distance”. ● Usually quite complex interconnections of sub-networks which are owned by different operators ● No broadcast, but point-to-point connections ● Range: several 1000 km ● Examples: WAN ● Frame Relay ● Asynchronous Transfer Mode (ATM) ● Synchronous Digital Hierarchy (SDH)

Univ. -Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.115 Transmission Technologies for WANs

● Point-to-Point Links ● Provision of a single WAN connection from a customer to a remote network ● Example: telephone lines. Usually communication resources are leased from the provider. ● Accounting is based on the leased capacity and the distance to the receiver. ● Circuit Switching ● A connection is established when required, communication resources are reserved exclusively. After the communication process, the resources are released. ● Example: Integrated Services Digital Network (ISDN) ● Packet Switching ● “Enhancement” of the “Circuit Switching” and the Point-to-Point links. ● Shared usage of the resources of one provider by several users, i.e., one physical connection is used by several virtual resources. ● Shared usage reduces costs

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.116 Transmission Technologies for WANs

● Circuit Switching ● Reservation of resources for the time of the connection

● Packet Switching ● Sharing of the resources

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.117 Packet Switching

● Packet Switching is the most common communication technology in WANs today ● The provider of communication resources provides virtual connections (virtual circuits, circuit switching) between remote stations/networks, the data are transferred in the form of packets. ● Examples: Frame Relay, ATM, OSI X.25

● Two types of Virtual Circuits: ● Switched Virtual Circuits (SVCs) ● Useful for senders with sporadic transmission wishes. ● A virtual connection is established, data are transferred, after the transmission the connection is terminated and the resources are released. ● Permanent Virtual Circuits (PVCs) ● Useful for senders which need to transfer data permanently. ● The connection is established permanently, there exists only the phase of the data transfer.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.118 Frame Relay

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.119 Frame Relay Network Implementation

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.120 Frame Relay

● Based on Packet Switching, i.e., the transmission of data packets ● Originally designed for the use between ISDN devices, usage has spread further ● The packets can have variable length ● Statistical Multiplexing (i.e. “mixing” of different data streams) for controlling the network access. ● This enables a flexible, efficient use of the available bandwidth ● A first standardization took place 1984 by the CCITT. However, it did not result in a complete specification. ● Therefore, in 1990 Northern Telecom, StrataCom, Cisco, and DEC formed a consortium that build up upon the incomplete specification and developed some extensions to Frame Relay which should make a usage in the complex Internet environment possible. These extensions were called Local Management Interface (LMI) Due to their success, ANSI and CCITT standardized own LMI variants ● Frame Relay finally became internationally standardized by the ITU-T, in the USA by ANSI.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.121 Structure of Frame Relay

● Purpose: simple, connection-oriented technology for economic transmission of data with acceptable speed ● Data transmission rates of 56 Kbps up to 45 Mbps can be leased ● Mostly used for permanent virtual connections for which no signaling for the connection establishment is necessary ● Two device categories can be distinguished: ● Data Terminal Equipment (DTE) typically in the possession of the end user, for example PC, router, bridges, … ● Data Circuit-Terminating Equipment (DCE) in the possession of a provider. DCEs realize the transmission process. Usually they are implemented as packet switches.

DTE DTE DCE

DTE

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.122 Communication within Frame Relay

● Frame Relay offers connection-oriented communication on the LLC layer: ● Between two DTEs a virtual connection is established. It is identified by a unique connection identifier (Data-Link Connection Identifier, DLCI). ● Note: DLCIs only refer to one hop, not to the entire connection; in addition they are only unique in a LAN, not globally:

DLCI DLCI

12 22

27 45 DTE 62 36 DTE

89 62

● The virtual connection offers a bidirectional communication path. ● Several virtual connections can be multiplexed to a single physical connection (reduction of equipment and network complexity).

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.123 Communication within Frame Relay

● Frame Relay offers two types of connections ● Switched Virtual Circuits (SVC) ● Temporary connections used when sporadic data transfer between DTEs is required ● Four states ● Call setup: Establish virtual circuit between two DTEs ● Data transfer: Transmit data ● Idle: Connection is active, but no data to transfer ● Call termination: Bring down the virtual circuit ● Permanent Virtual Circuits (PVC) ● Permanent established connections for consistent data transfers between DTEs ● Do not require a call setup, two states ● Data transfer: Transmit data ● Idle: No data to transfer  Small protocol overhead, high data transmission rates

Univ. -Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.124 Flow Control within Frame Relay

● Flow Control in Frame Relay ● Frame Relay does not possess an own flow control mechanism for controlling the traffic of each virtual connection. ● Frame Relay is used typically on reliable network media, therefore flow control can be left over to higher layers. ● Instead: Notification mechanism (Congestion Notification) to report bottlenecks to higher protocol layers, if a control mechanism on a higher layer is implemented. ● There are two mechanisms for Congestion Notification: ● Forward-Explicit Congestion Notification (FECN) ● Initiated, when a DTE sends frames into the network ● In case of overload, the DCEs (switches) in the network set a special FECN bit to 1 ● If the frame arrives at the receiver with set FECN bit, it recognizes that an overload on the virtual connection is present. The information is relayed to higher layers. ● Backward-Explicit Congestion Notification (BECN) ● Similarly to FECN, but the BECN bit is set in frames which are transmitted in the opposite direction from frames with set FECN bit

Univ. -Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.125 Asynchronous Transfer Mode (ATM)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.126 ATM for the Integration of Data and Telecommunication

Telecommunication Data communication ● Primary goal: Telephony ● Primary goal: Data transfer ● Connection-oriented ● Connectionless ● Firm dispatching of resources ● Flexible dispatching of resources ● Performance guarantees ● No performance guarantees ● Unused resources are lost ● Efficient use of resources ● Small end-to-end delay ● Variable end-to-end delay

Time Division Multiplexing Statistical Multiplexing

bandwidth allocation bandwidth allocation

t t

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.127 Characteristics of ATM

● Characteristics of ATM ● ITU-T standard (resp. ATM forum) for cell transmission ● Integration of data, speech, and video transmissions ● Combines advantages of ● Circuit Switching (granted capacity and constant delay) ● Packet Switching (flexible and efficient transmission) ● Cell-based Multiplexing and Switching technology ● Connection-oriented communication: virtual connections are established ● Guarantee of quality criteria for the desired connection (bandwidth, delay, …) ● For doing so, resources are being reserved in the switches. ● No flow control and error handling ● Supports PVCs, SVCs, and connection-less transmission ● Data rates: 34, 155, or 622 Mbps (optical fiber)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.129 ATM Cells ● No packet switching, but Cell cell switching: like time Payload division multiplexing, but header without reserved time slots 48 byte 5 byte ● Fix cell size: 53 byte

Cell multiplexing on an ATM connection:

● Asynchronous time multiplexing of several virtual connections ● Continuous cell stream ● Unused cells are sent empty ● In overload situations, cells are discarded

2 2 1 3 2 3 2

3 3 empty cell

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.130 Cell Size: Transmission of Speech

Coding audio: Pulse-code modulation (PCM) Example (simplification: Quantization with 3 bits) ● Transformation of analogous Origin signal Interval Reconstructed signal Binary into digital signals number code ● Regular scanning of the + 4 111 analogous signal + 3 110 Scanning error ● Scanning theorem + 2 101 (Nyquist): + 1 100 Scanning rate  2×cutoff - 1 000 frequency of the original signal T - 2 001

Cutoff frequency of a range Quantization telephone: 3.4 kHz - 3 011  scanning rate of 8000 Hz - 4 010 ● Each value is quantized with 8 Scanning Time bits (i.e. a little bit rounded). Intervals ● A speech data stream therefore

has a data rate of 1 0 0 1 0 1 1 1 1 1 1 1 1 0 0 0 1 0 0 1 1 0 0 1 8 bits × 8000 1/s = 64 kbps produced pulse code

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.131 Cell Size within ATM

Problem: Delay of the cell stream for speech is 6 ms 48 samples with 8 bits each = 48 byte = Payload for an ATM cell Larger cells would cause too large delays during speech transmission t=125 ms Smaller cells produce too much overhead for “normal” data (relationship Header/Payload) Continuous data stream with i.e. 48 byte is a compromise. scanning rate 1/125 ms

TD = 6 ms

header packetisation overhead delay 100% 10ms

50% 5ms 64+5 32+4 48+5 0 20 40 60 80 cell size [bytes]

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.132 ATM Network

● Two types of components: ● ATM Switch ● Dispatching of cells through the network by switches. The cell headers of incoming cells are read and information is updated. Afterwards, the cells are switched to the destination. ● ATM Endpoint ● Contains an ATM network interface adapter to connect different networks with the ATM network.

ATM Endpoints Router

LAN switch ATM network

ATM switch Workstation

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.133 Structure of ATM cells

● Two header formats: ● Communication between switches and endpoints: User-Network Interface (UNI) ● Communication between ATM switches in private networks ● Communication between two switches: Network-Network Interface (NNI)

7 6 5 4 3 2 1 0 GFC/VPI VPI VPI VCI

PTI CLP HEC

Payload (48 bytes)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.134 Structure of ATM cells

● Header Fields 7 6 5 4 3 2 1 0 ● Generic Flow Control (GFC) GFC VPI ● Only with UNI, for local control of the VPI transmission of data into the network. ● Virtual Path Identifier (VPI)/ VCI Virtual Channel Identifier (VCI) PTI CLP ● Identification of the next destination of HEC the cell ● Payload Type Identifier (PTI) ● Describes content of the data part, e.g., user data or different control data 7 6 5 4 3 2 1 0 ● Cell Loss Priority (CLP) VPI ● If the bit is 1, the cell can be discarded in overload situations. VCI ● Header Error Control (HEC) PTI CLP ● CRC for the first 4 bytes; single bit errors can be corrected. HEC

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.135 Connection Establishment in ATM

● The sender sends a connection establishment request to its ATM switch, containing the ATM address of the receiver and demands about the quality of the transmission. ● The ATM switch decides on the route, establishes a virtual connection (assigning a connection identifier) to the next ATM switch and forwards (using cells) the request to this next switch. ● When the request reaches the receiver, it sends back the established path and acknowledgement. ● After establishment, ATM addresses are no longer needed, only virtual connection identifiers are used.

Establish connection to EC 23.0074.4792.783c.7782.7845.0092.428c.c00c.1102.01 EC OK OK EC EC

OK ATM address OK 23.0074.4792.783c. 7782.7845.0092.428 c.c00c.1102.01

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.136 ATM Switching

● Before the start of the communication a virtual connection has to be established. The switches are responsible for the forwarding of arriving cells on the correct outgoing lines. For this purpose a switch has a switching table.

Switching Table Incoming lines Switch Outgoing lines In Old Out New Header Header 1 1

2 2 1 a n a ...

... 2 c n d

......

...

n n n b 2 e

● The header information, which are used in the switching table are VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier). ● If a connection is being established via ATM, VPI, and VCI are assigned to the sender. Each switch on the route fills in to where it should forward cells with this information.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.137

Path and Channel Concept of ATM

● Physical connections “contain” Virtual Paths (VPs, a group of connections)

● VPs “contain” Virtual Channels (VCs, logical channels)

● VPI and VCI only have local significance and can be changed by the switches. ● Distinction between VPI and VCI introduces a hierarchy on the path identifiers. Thus: Reduction of the size of the switching tables.

There are 2 types of switches in the ATM network:

Virtual Path Switching Virtual Channel Switching

VP Switch VC Switch VCI 1 VCI 3 VPI 1 VPI 4 VCI 2 VCI 4 VCI 1 VCI 3 VCI 4 VCI 2

VCI 3 VCI 5 VPI 5 VCI 4 VPI 2 VCI 6

VPI 2 VCI 2 VCI 1 VCI 5 VPI 6 VPI 3 VCI 2 VPI 1 VCI 6 VPI 3 VCI 4

VP-SWITCH VP/VC-SWITCH

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.138 Layers within ATM

● Physical Layer ● Transfers ATM cells over the medium ● Generates checksum (sender) and verifies it (receiver); discarding of cells ● ATM Layer ● Generates header (sender) and extract contents (receiver), except checksum ● Responsible for connection identifiers (Virtual Path and Virtual Channel Identifier) ● ATM Adaptation Layer (AAL) ● Adapts different requirements of higher layer applications to the ATM Layer ● Segments larger messages and reassembles them on the side of the receiver

Station Station

Higher Layers Higher Layers

ATM Adaptation ATM Adaptation Layer Switch Switch Layer ~DLL of OSI ATM Layer ATM Layer ATM Layer ATM Layer

Physical Layer Physical Layer Physical Layer Physical Layer

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.139 Service Classes of ATM

Service Class Criterion A B C D

Negotiated Maximum and Dynamic “Take what Data rate maximum average rate adjustment you can cell rate cell rate to free get” resources Synchronization Yes No (source - destination) Bit rate constant variable

Connection Connection-oriented Connectionless Mode

Applications: . Moving pictures . Data communication . Telephony . File transfer . Video conferences . Mail

AAL 3 AAL 4 Adaptation Layer (AAL): AAL 1 AAL 2 AAL 5

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.140 AALs

Load AAL 1: Constant Bit Rate (CBR) PCR ● Deterministic service ● Characterized by guaranteed fixed bit rate ● Parameter: Peak Cell Rate (PCR)

AAL 2: Variable Bit Rate (VBR) ● Real time/non real time, statistical service Load Time ● Characterized by guaranteed average bit rate. Thus also suited for bursty traffic. PCR ● Parameter: Peak Cell Rate (PCR), Sustainable Cell Rate SCR (SCR), Maximum Burst Size

AAL 3: Available Bit Rate (ABR) ● Load-sensitive service ● Characterized by guaranteed minimum bit rate and load- Load Time sensitive, additional bit rate (adaptive adjustment) ● Parameter: Peak Cell Rate, Minimum Cell Rate ABR/ UBR AAL 4: Unspecified Bit Rate (UBR) ● Best Effort service Other ● Characterized by no guaranteed bit rate connec- ● Parameter: Peak Cell Rate tions Time

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.141 Services Classes of ATM

100% Available Bit Rate (ABR)

Unspecified Bit Rate (UBR)

Capacity

Variable Bit Rate (VBR) Line

Constant Bit Rate (CBR)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.142 Traffic Management

● Connection Admission Control (CAC) ● Reservation of resources during the connection establishment (signaling) ● Comparison between connection parameters and available resources ● Traffic contract between users and ATM network ● Usage Parameter Control/Network Parameter Control ● Test on conformity of the cell stream in accordance with the parameters of the traffic contract at the user-network interface (UNI) or network-network interface (NNI) ● Generic Cell Rate Algorithm/Leaky Bucket Algorithm ● Switch Congestion Control (primary for UBR) ● Selective discarding of cells for the maintenance of performance guarantees in the case of overload ● Flow Control for ABR ● Feedback of the network status by resource management cells to the ABR source, for the adjustment of transmission rate and fair dispatching of the capacity

Univ. -Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.143

Integration of ATM into Existing Networks

● What does ATM provide? ● ATM offers an interface to higher layers (similar to TCP in the Internet protocols) ● ATM additionally offers QoS guarantees (Quality of Service) ● ATM had problems during its introduction ● Very few applications which build directly upon ATM ● In the interworking of networks TCP/IP was standard ● Without TCP/IP binding, ATM could not be sold! ● Therefore different solutions for ATM were suggested, e.g. ● IP over ATM (IETF) ● LAN emulation (LANE, ATM forum)

● Today: ATM still is in use in some regions, but SDH (as a technology coming from the telecommunication sector) took over the leading role in WAN technology

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.144 Synchronous Digital Hierarchy (SDH)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.145 Synchronous Digital Hierarchy (SDH)

● All modern networks in the public “Dark Fiber” area are using the SDH technology rented wavelength ● Example: the German B-WIN (ATM) was replaced by the G-WIN GRE HAM KIE ROS (Gigabit-Wissenschaftsnetz) AWI DES EWE on basis of SDH FFO BRE TUB POT PSNC ● Since 2006: X-WIN – complete HAN HUB MUE BIE redesign of topology, additionally Surfnet BRA MAG ZIB ADH integration of DWDM (dense DUI KAS GOE LEI wavelength division multiplexing): FZJ MAR DRE AAC BIR JEN up to 160 parallel transmissions GIE CHE over a fiber, giving 1.6 Tbps Geant2 FRA ILM GSI BAY capacity! WUE ESF HEI ERL REG ● Also used within the MAN range SAA FZK (Replaced by Gigabit Ethernet?) Renater KEH AUG STU ● Analogous technology in the USA: GAR Switch/GARR Synchronous Optical Network (SONET)

Univ. -Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.146 Synchronous Digital Hierarchy (SDH)

● Introduction of PCM in the 1960s ● Digital telephone system ● Before SDH was introduced Plesiochronous Digital Hierarchy (PDH) was used ● Europe: Combination of 30 channels of 64kbps ● USA, Canada, Japan: Combination of 24 channels of 64kbps

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.147 SDH Structure

● SDH achieves higher data rates than ATM (at the moment up to about 40 Gbps) ● Flexible capacity utilization and high reliability ● Structure: arbitrary topology, meshed networks with a switching hierarchy (exemplarily 3 levels):

Synchronous Digital(SDH) Synchronous Hierarchy

Supraregional switching 2.5 Gbps SDH Cross Connect 155 Mbps Regional switching centers 155 Mbps

Add/Drop Multiplexer

34 Mbps

Local networks 2 Mbps

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.148 Multiplexing within SDH

2 Mbps, 155 Mbps 622 Mbps 2.5 Gbps 10 Gbps 34 Mbps,…

+ control information for signaling

Switching center 34 Mbps

622 Mbps 2 Mbps 2 Mbps

Switching 622 Mbps SDH Cross Connect center 155 Mbps

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.149 Characteristics of SDH

● World-wide standardized bit rates on the hierarchy levels ● Synchronized, centrally clocked network ● Multiplexing of data streams is made byte-by-byte, simple multiplex pattern ● Suitable for speech transmission: ● Since on each hierarchy level four data streams are mixed byte-by-byte and a hierarchy level has four times the data rate of the lower level, everyone of these mixed data streams has the same data rate as on the lower level. Thus the data experience a constant delay. ● Direct access to signals by cross connects without repeated demultiplexing ● Short delays in inserting and extracting signals ● Additional control bytes for network management, service and quality control,… ● Substantial characteristic: Container for the transport of information

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.150 SDH Architecture

● Physical Layer ● Transmission medium, typically fiber optics PSTN/ISDN ATM IP ● Radio and Satellite links VC-12 Layer   ● Regenerator Section VC-4 Layer ● Path between regenerators Multiplex Section ● Multiplex Section Regenerator Section ● Link between multiplexers Physical Layer ● VC Layer (Virtual Container) ● Part of the mapping procedure, i.e., 140Mbps packing of ATM and PDH signals 2Mbps into SDH

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.151 Components of a SDH Network

● Four different types of network elements ● Regenerators ● Regenerate incoming signal (clock and amplitude) ● Clock signal is derived from incoming signal ● Terminal multiplexer ● Combine PDH and SDH signals into higher bit rate STM signals ● Add/drop multiplexer ● Insert or extract PDH and SDH lower bit rate signals ● Digital cross connects ● Mapping of PDH tributary signals into virtual containers ● Switching of various containers

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.152 Components of a SDH Network

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.153 Synchronization in SDH

● All network elements have to be synchronized ● Central clock with high accuracy, i.e., 1 x 10-11 ● Primary Reference Clock (PRC) ● Clock signal is distributed in the network ● Hierarchical structure to distribute clock signals ● Subordinate synchronization supply units (SSU) ● Synchronous equipment clocks (SEC) ● Synchronization path can be the same as for data

PRC G.811

SSU SSU G.812 G.812

SEC SEC SEC SEC G.813 G.813 G.813 G.813

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.154 SDH Transport Module (Frame) 270 columns (bytes) Synchronous Transport Module (STM-N, N=1,4,16, 64) 9 columns (bytes) 261 columns (bytes)

STM-1 structure: 1 Regenerator Section Overhead (RSOH) . 9 lines with 270 bytes each 3 9 lines 4 Administrative Unit Pointers Payload . Each byte in the payload (125 µs) represents a 64 kbps channel 5 Multiplex Section . Basis data rate of 155 Mbps Overhead (MSOH) 9 9x270x8x8000 bps = 155.52 Mbps

Administrative Unit Pointers . Permit the direct access to components of the Payload Section Overhead . RSOH: Contains information concerning the route between two repeaters or a repeater and a multiplexer . MSOH: Contains information concerning the route between two multiplexers without consideration of the repeaters in between. Payload . Contains the utilizable data as well as further control data

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.155 Creation of a STM

● Creation of a Synchronous Transport Module (STM) ● Payload is packed into a container ● A distinction of the containers is made by size: C-1 to C-4 ● Payload data are adapted if necessary by padding to the container size ● Some additional information to the payload are added for controlling the data flow of a container over several multiplexers ● Path Overhead (POH) ● Control of single sections of the transmission path ● Change over to alternative routes in case of an error ● Monitoring and recording of the transmission quality ● Realization of communication channels for maintenance ● By adding the POH bytes, a container becomes a Virtual Container (VC)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.156 Creation of a STM

● If several containers are transferred in a STM payload, these are multiplexed byte-by-byte in Tributary Unit Groups (TUG). ● By adding an Administrative Unit Pointer, the Tributary Unit Group becomes an Administrative Unit (AU). ● Then the SOH bytes are supplemented, the SDH frame is complete. RSOH and MSOH contain for example bits for ● Frame synchronization ● Error detection (parity bit) ● STM-1 identifications in larger transportation modules ● Control of alternative paths ● Service channels ● … and some bits for future use

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.157 SDH Hierarchy

155 Mbps 622 Mbps 2.5 Gbps

STM-1 STM-4 STM-16

261 4x261=1044 4x1044=4176 9 4x9=36 4x36=144

Assembled from Assembled from

Basis transportation module for 4 x STM-1 4 x STM-4 155 Mbps, e.g. contains: . a continuous ATM cell stream (C-4 container) . a transportation group (TUG-3) Assembled from for three 34 Mbps PCM systems . a transportation group (TUG-3) 4 x STM-1 for three containers, which again contain TUGs

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.158 SDH Hierarchy

● Higher hierarchy levels assembling STM-1 modules ● Higher data rates are assembled by multiplexing the contained signals byte-by- byte ● Each byte has a data rate suitable of 64 kbps for the transmission of voice (telephony) ● Except STM-1, only transmission over optical fiber is specified

9 columns

261 byte

4 * 261 byte 4 * 9 columns

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.159 Types of SDH Containers

C-n Container n Payload VC-n Virtual Container n Tributary Unit, n (n=1 to 3) TU-n Tributary Unit n . Contains VC-n and Tributary Unit TUG-n Tributary Unit Group n Pointer

C-4 VC-4 TUG-3 3 2 1 H4 or VC-3

VC-4 Path Overhead (POH)

Container, C-n (n=1 to 4) Virtual Container, VC-n (n=1 to 4) . Defined unit for payload capacity (e.g. C-4 . Consists of container and POH for ATM or IP, C-12 for ISDN or 2 Mbps) . Lower VC (n=1,2): single C-n plus basis . Transfers all SDH bit rates Virtual Container Path Overhead (POH) . Capacity can be made available for transport . Higher VC (n=3,4): single C-n, union from broadband signals not yet specified of TUG-2s/TU-3s, plus basis Virtual Container POH

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.160 Types of SDH Containers

● Virtual Containers (VC)

SDH Bit Rate [Mbps] Size of VC Rows x Columns VC-11 1,728 9 x 3 VC-12 2,304 9 x 4 VC-2 6,912 9 x 12 VC-3 48,960 9 x 85 VC-4 150,336 9 x 261

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.161 Types of SDH Containers

VC-3 C-n Container n VC-n Virtual Container n TU-n Tributary Unit n TUG-n Tributary Unit Group n TU-3 7 AU-n Administrative Unit n 6 or 5 STM-N Synchronous 4 C-3 3 Transport Module N 2 1

VC-2 TUG-2 Administrative Unit n (AU-n)

3 . Adaptation between higher order 2 VC-12 path layer and multiplex unit 1 TUG-12 C-12 . Consists of payload and Administrative Unit Pointers

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.162 SDH Multiplex Structure

x N STM-N AUG AU-4 VC-4 C-4 x 3

x 3 TUG-3 TU-3 VC-3

C-3 AU-3 VC-3 x 7 x 7 TUG-2 TU-2 VC-2 C-2 Pointer Processing x 3 Multiplexing TU-12 VC-12 C-12 C-n Container n x 4 VC-n Virtual container n TU-11 VC-11 C-11 TU-N Tributary Unit n TUG-n Tributary Unit Group n AU-n Administrative Unit n AUG Administrative Unit Group STM-N Synchronous Transport Module N

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.163 SDH Multiplexing

Container-1 Logical association Physical association VC-1 POH Container-1 VC-1 PTR Pointer

TU-1 PTR VC-1 TU-1

(1) PTR (2) PTR (3) PTR (4) PTR VC-1 (1) VC-1 (2) VC-1 (3) VC-1 (4) TUG-2

VC-3 POH TUG-2 TUG-2 VC-3

AU-3 PTR VC-3 AU-3

AU-3 PTR AU-3 PTR VC-3 VC-3 AUG

SOH AUG AUG STM-N

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.164 What can SDH achieve?

SONET SDH Data rate (Mbps) Electrical Optical Optical Gross Net STS-1 OC-1 STM-0 51.84 50.112 STS-3 OC-3 STM-1 155.51 150.336 STS-9 OC-9 (STM-3) 466.56 451.008 STS-12 OC-12 STM-4 622.08 601.344 STS-18 OC-18 (STM-6) 933.12 902.016 STS-24 OC-24 (STM-8) 1,244.16 1,202.688 STS-36 OC-36 (STM-12) 1,866.24 1,804.032 STS-48 OC-48 STM-16 2,488.32 2,405.376 STS-96 OC-96 STM-32 4,976.64 4,810.752 STS-192 OC-192 STM-64 9,953.28 9,621.504 STS-768 OC-758 STM-256 39,813.12 38,486.016

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.165 Network Infrastructure

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.166 Network Infrastructure

● For building computer networks more complex than a short bus, some additional components are needed: ● Repeater ● Physically increases the range of a local area network ● Hub ● Connects several computers or local area networks of the same type (to a broadcast network) ● Bridge ● Connects several local area networks (possibly of different types) to a large LAN ● Switch ● Like a hub, but without broadcast ● Router ● Connects several LANs with the same network protocol over large distances ● Gateway ● Understands two different technologies and can convert the contents from one to the other and vice versa

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.167 Network Infrastructure

Application layer Application gateway Packet from network layer

Transport layer Transport gateway Frame Packet TCP User Network layer Router CRC header header header data Data link layer Bridge, Switch

Physical layer Repeater, Hub Frame in Data link layer

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.168 Infrastructure Components: Hub & Repeater ● Transmission of data on the physical layer ● Reception and refreshment of the signal, i.e., the signals received on one port are newly produced on the other(s) Layer 1 ● Do not understand frames, packets, or headers ● Increase of the network range ● Stations cannot send and receive at the same time ● One shared channel (Broadcast) ● Low security, because all stations can monitor the whole traffic ● Low costs

Hub

Segment 1

Repeater

Segment 2 Repeater: Linking of 2 Hub: “one to all” networks

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.169 Infrastructure Components: Hub & Repeater

Hub

Device1 Hub

Device2

Device3

. . . Devicen

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.170 Infrastructure Components: Bridge

● Bridge ● Bridge connects 2 or more LANs Layer 2 ● Operates on frame addresses ● Can support different network type

Upper Layer (Bridge protocol, Bridge management) Data path Control path LLC LLC MAC1 MAC-Relay MAC2

PHY PHY

Network1 Network 2 MAC1 Data LLC MAC1 MAC2 Data LLC MAC2

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.171 Bridging

● Typically a LAN comes rarely alone ● What to do if many LANs exist? ● Connect them by bridges ● A bridge examines the data link layer address for routing ● Reasons why one organization could have multiple LANs ● Autonomy of the owner ● Several buildings with each having a LAN ● Machines are too distant ● Ethernet supports only up to 2.5 km ● Load ● Security ● Reliability ● Requirements: ● Bridges should be transparent ● Moving of machines from one segment to another must not require the change of software or hardware

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.172 Network Infrastructure

● Bridges from 802.x to 802.y

● Problems when moving frames between LANs ● Different frame formats ● Different data rates ● Different max. frame length ● Security: Some support encryption others do not ● Quality of Service

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.173 Infrastructure Components: Bridges

● With bridges, several LANs are connected on the link layer – possibly LANs of different types, i.e., having different header formats ● Major tasks: ● Appropriate forwarding of the data ● Adaptation to different LAN types ● Reduction of the traffic in a LAN segment, i.e., packets which are sent from A to C are not forwarded by the bridge to LAN2. Thus, station D can communicate with E in parallel. ● Increases physical length of a network ● Increased reliability through demarcation of the LAN segments

A C D E B1

LAN1 LAN2

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.174 Infrastructure Components: Bridges

● Transparent bridges (e.g. for CSMA and Token Bus networks)

A C B D B E 1 ²

LAN1 LAN2 LAN3

● Characteristics ● Coupling of LANs is transparent for the stations, i.e., not visible ● Hash tables contain the destination addresses ● Routing Procedure ● Source and destination LAN are identical  frame is rejected by bridge, e.g., B1 in case of a transmission from A to C ● Source and destination LAN are different  forward frames, e.g., in case of a transmission from D to E ● Destination LAN unknown  flood frame

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.175 Transparent Bridges

. To realize transparency, bridges have to learn in which LAN a host is located . Each bridge maintains a forwarding database with entries  MAC address: host name  port: port number of bridge used to send data to the host  age: aging time of entry

. Assume a MAC frame arrives on port x: Port x

Bridge 2 Is MAC address of Port A Port C Port B destination in forwarding database for ports A, B, or C?

Found and  x? Not found ? Found and = x?

Forward the frame on the Flood the frame, i.e., send the Ignore frame appropriate port frame on all ports except port x.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.176 Transparent Bridges: Address Learning

● Database entries are set automatically with a simple heuristic ● the source field of a frame that arrives on a port tells which hosts are reachable from this port. ● Algorithm: ● For each frame received, the source stores the source field in the forwarding database together with the port where the frame was received. ● All entries are deleted after some time (default is 15 seconds).

Src=x, SrcSrc=x,Src=y,=x, Dest=y Port 1 Port 4 DestDest=yDest=x=y x is at Port 3 Src=x, y is at Port 4 Src=x, Dest=y Port 2 Port 5 Dest=y

Src=x, Src=x,SrcSrc=y,=x, Dest=y Dest=xDest=yDest=y Port 3 Port 6

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.177 Loops

● Consider two LANs that are connected by two bridges. ● Assume host n is transmitting a LAN 2 frame F with unknown destination. ● Bridges A and B flood the frame F F to LAN 2. ● Bridge B sees F on LAN 2 (with Bridge A Bridge B unknown destination), and copies F F the frame back to LAN 1 ● Bridge A does the same. LAN 1 ● The copying continues F

● Solution: Spanning Tree Algorithm host n

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.178 Spanning Tree Bridges

● Preventing loops: compute a spanning tree from all connected LAN 2 bridges d

Bridge 3 Bridge 4 ● Spanning Tree Algorithm: ● Determine one root bridge LAN 5 ● The bridge with the smallest ID Bridge 1 ● Determine a designated bridge for Bridge 5 each LAN ● The bridge which is nearest to the root bridge LAN 1 ● Determine root ports ● Port for the best path to root bridge Bridge 2 considering costs for using a path, e.g., the number of hops. LAN 3 LAN 4

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.179 Spanning Tree Algorithm

● At the beginning, all bridges assume to be root bridge and send out a packet containing their own ID and current costs (initialized with zero) over all of their ports: root ID costs bridge ID port ID

e.g. for station B on port P : 1

B 0 B P1

● A bridge receiving such a packet checks the root ID and compares it with its own one. Root ID and costs are updated for received packets with smaller ID in the root bridge field and forwarded. Updating the costs is made by adding the own costs for the station from which the packet was received to the current costs value. ● When the (updated) packets of all bridges have passed all other bridges, all bridges have agreed on the root bridge. The received packets containing the smallest costs value to the root bridge determine the designated bridge for a LAN and designated ports for the bridges to send out data.

Univ. -Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.180

Spanning Tree Algorithm: Example

B1 B3 Network: LAN 1 12 10 7 LAN 2 ID=93 ID=18 20 5 B2 B4 5 LAN 3 5 ports ID=27 ID=3 8 10 ID: bridge ID : designated port B5 LAN 4 6 10 LAN 5 ID=9

Spanning Tree: B1 B3 LAN 1 LAN 2 ID=93 ID=18 designated bridge for LAN 2 B2 B4 LAN 3 ID=27 ID=3 root bridge B5 LAN 4 LAN 5 ID=9

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.181 Infrastructure Components: Bridges

● Source Routing Bridges (e.g. for ring networks)

A D B B 1 FDDI ²

Ethernet Ethernet

● Characteristics: ● Sources must know (or learn), in which network segment the receivers are located ● Large expenditure for determining the optimal route, e.g., via using a Spanning Tree algorithms or sending out Route Discovery Frames using broadcast ● All LANs and Bridges on the path must be addressed explicitly ● Connection-oriented, without transparency for the hosts

Univ. -Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.182

Infrastructure Components: Switch

● Like a bridge, but: ● Point-to-point communication, no broadcast Layer 2/3/4 ● Switch learns the addresses of the connected computers ● Stations can send and receive at the same time ● No carrier control necessary ● Buffer for each individual Switch station/each port ● Higher costs . “Layer 3-Switch”: also has functionalities of level 3, i.e., it can e.g. take over the routing.

. “Layer 4-Switch”: looks up additionally in the TCP-header, can therefore be used e.g. for load balancing.

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.183 Infrastructure Components: Switch – Realization

● Mostly used: buffered crossbar ● For each input port, provide buffers for the output ports ● At any time, only one input port can be connected to an output line ● Additional speedup possible with small buffers at each cross-point ● With a buffered switch, nearly no more collisions are possible!

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.184 Switched LANs – Mechanismen

● Cut Through ● Adresstabelle wird angesprochen, sobald die Zieladresse eingelesen ist ● Weiterleitung des Datenpakets, sobald der Weg geschaltet ist ● Geringe Latenzzeit

● Store and Forward ● Datenpaket wird zunächst vollständig eingelesen und zwischengespeichert ● Kontrolle der CRC-Prüfsumme und Ausführen von Filterfunktionen

● Hybrides Switching ● Kombination von Cut Through / Store and Forward ● Auswahl abhängig von Fehlerrate

● Predictive Switching ● Pfad in Schaltmatrix wird hergestellt, bevor Zieladresse vollständig eingelesen ● Basierend auf den vorher geschalteten Pfaden

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.185 Infrastructure Components: Router

● What are the limitations of bridges? ● Even though bridges are suitable to connect computers in several networks, there are also some disadvantages, e.g.: ● Bridges can support only some thousand stations, which especially has the reason that addresses are used which do not have any geographical reference. ● LANs coupled with bridges already form a “large LAN”, although a separation often would be desirable (e.g. regarding administration or errors). ● Bridges pass broadcast frames on to all attached LANs. This can result in “Broadcast Storms”. ● Bridges do not communicate with hosts, i.e., they do not hand over information about overload situations or reasons for rejected frames. Router overcome these weaknesses

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.186 Infrastructure Components: Router

● Principal task of routers ● Incoming packets are being forwarded on the best path Layer 3 possible to the destination on the basis of a global address ● In principle no restriction concerning the number of hosts (hierarchical addressing) ● Local administration of the networks (ends at the router), Firewalls are possible ● Broadcasts are not let through by the routers, Multicast depending on the router ● Communication between host and router improves performance

A B R 1 R 2 R 3

Network1 Network2 LAN 1 LAN 2

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.187 Infrastructure Components: Gateway

● Transport Layer Gateways ● Connection of computers using different transport protocols, e.g., a computer using TCP/IP and one using ATM transport protocol ● Copies packets from one connection to another

● Application Layer Gateways ● Understand the format and contents of the data and translate messages from one format to another format, e.g., email to SMS

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.188 Virtual LANs

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.189 Virtual LANs

● Organization of LANs ● In early Ethernet days all computers were on one LAN ● With 10Base-T came new cabling in buildings ● Configuration of LAN logically rather than physically ● Requirement: Decoupling of the logical topology from the physical topology

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.190 Virtual LANs

● Management often requires structuring of LANs due to ● Different departments want different LANs ● Security ● Load ● Broadcast (broadcast storm)

● What happens if users move from one department to another? ● Rewire in hub/switch ● VLANs with VLAN-aware switches

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.191 Virtual LANs

A B C D A B C D

I M I M

J N J N

K O K O

L L

E F G H E F G H

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.192 Virtual LANs

● Virtual LANs require VLAN-aware switches ● VLANs are often named by colors (VLAN ID) ● Allows colored diagrams which show logical and physical topology at the same time ● VLAN-aware devices have to know about the VLANs ● Switch has a table which tells which VLAN is accessible via which port ● A port may have access to multiple VLANs ● How do a VLAN-switch know the VLANs? ● Assign every port of the device a VLAN ID ● Only machines belonging to the same VLAN can be attached ● Every MAC address is assigned to a VLAN ● Device needs tables of the 48-bit MAC addresses assigned to VLANs ● Every Layer 3 protocol (IP address) is assigned to a VLAN ● Violates the independency of layers

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.193 Virtual LANs

● IEEE 802.1Q ● Special field in frame header telling the VLAN assignment ● Problems: ● What happens with existing Ethernet cards? ● Who generates the new field? ● What happens with full frames (maximum length)? ● Solution: ● The first VLAN-aware device adds a VLAN-tag ● The last VLAN-aware device removes the VLAN-tag

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.194 Virtual LANs

● IEEE 802.1Q Frame Format ● Additional pair of 2-byte fields ● TPID: Tag Protocol Identifier (0x8100) ● Tag comprises three fields ● Pri: 3-bit priority field, does not have anything to do with VLANs ● CFI: Canonical Format Indicator ● Indicates that payload has a IEEE 802.5 frame ● VLAN ID: 12-bit VLAN identifier ● The only relevant field

Preamble SFD DA SA L/T Data Padding FCS

Preamble SFD DA SA TPID Tag L/T Data Padding FCS

Pri CFI VLAN ID

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.195 Virtual LANs

● Who inserts the VLAN-tag? ● New cards (Gigabit Ethernet) support 802.1Q ● Otherwise ● First VLAN-aware switch adds the tag ● Last VLAN-aware switch removes the tag ● How does the switch know which frame belongs to which VLAN? ● First device has to decide based on the port or MAC address

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.196 Summary

● Layer 1 and 2: “How to physically transport data reliably from one computer to a neighbored one”? ● Layer 1 defines transmission medium and bit representation on this medium ● Layer 1 additionally specifies transmission mode, data rate, pin usage of connectors, … ● Layer 2 protects against transmission errors (mostly CRC) and receiver overload (flow control, sliding window) ● Layer 2 also defines medium access coordination for broadcast networks ● Both layers together define how to transfer data from one computer to a directly connected one (maybe over a hub/switch) – on that reason both are implemented in one piece of software: the network interface card driver. ● Bridges in principle allow to connect lots of LANs over long distances – is that the Internet?

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.197 Summary

● LANs ● Ethernet as standard for local networks ● 10G-Ethernet also possible for use in MANs ● WANs ● SDH/Sonet as standard for wide area networks ● 10G-Ethernet as access technology to the core network ● Integration of DWDM – transmission on 160 wavelengths in parallel dramatically increases the capacity ● Also possible: SDH with 40 Gbps, DWDM with 4096 channels – 164 Tbps! ● Dream of “all optical network”: switch/route data streams with optical components (think of a prism)

Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.198